Cancer (tumor) is the number one cause of death in Japan. According to the statistics from the Center for Cancer Control and Information Services in independent administrative institution the National Cancer Center, Japan, the number of people who died of cancer in 2006 was approximately 329,000. On a site basis, the number for men increases in the order of lung (23%), stomach (17%), liver (11%), colon (7%, or 11% as the whole of the large intestine), and pancreas (6%), while the number for women increases in the order of stomach (13%), lung (13%), colon (10%, or 14% as the whole of the large intestine), breast (9%), and liver (8%). The number of patients is increasing year after year, and development of highly effective and safe drugs and treatment methods are strongly desired.
Gastric cancer is one of cancers which are very high in both of morbidity rate and mortality rate in Japan, but is now also considered as one of cancers which are relatively easy to cure by advancement in diagnostic methods and treatment methods mainly including chemotherapy and surgical resection through operation. However, scirrhous gastric cancer is considered as one of highly malignant gastric cancers which are difficult to treat. Scirrhous gastric cancer has the following characteristics. The cancer cells do not appear on the surface of a mucous membrane, but diffusely infiltrate the entire stomach wall or half to ⅓ or more thereof. The scirrhous gastric cancer thickens and hardens the stomach wall without forming tumoral mass which is obvious with naked eyes. Further, the boundary between the lesion and the surrounding mucous membrane is unclear. Scirrhous gastric cancer progresses faster than usual gastric cancers even if the age of onset is young, and is also difficult to diagnose. At the time when the diagnosis is made, peritoneal dissemination or metastasis has already occurred and no operation is available in 60% of the cases. Even if resection is performed by a surgery, the five-year survival rate is only 15 to 20%.
Recently, the importance of a use of an antibody as an anti-cancer agent is increasingly recognized as an approach in treating various disease conditions (of cancer types). For example, in a case of an antibody targeting a tumor-specific antigen, the antibody thus administrated is assumed to accumulate at the tumor. Accordingly, attack on cancer cells can be expected by an immune system through complement-dependent cytotoxicity (CDC) or antibody-dependent cell-mediated cytotoxicity (ADCC). Moreover, by binding an agent such as a radionuclide or cytotoxic substance to an antibody in advance, the agent thus bound can be efficiently transferred to a tumor site. Thereby, the amount of the agent reaching to the other tissues can be reduced, and consequently reduction in side effect can be expected. By administering an antibody having an agonistic activity in a case where a tumor-specific antigen has an activity to induce cell death, or by administering an antibody having a neutralizing activity in a case where a tumor-specific antigen is involved in cell growth and survival, termination or shrinkage of tumor growth can be expected from the accumulation of the tumor-specific antibody and the activity of the antibody. Because of such abilities, it is thought that an antibody is suitably applied as an anti-cancer agent.
As antibody drugs having being put on the market so far for leukemia and lymphoma, rituximab (product name rituxan) and iburitumomab tiuxetan (product name Zevalin) targeting CD20, gemtuzumab ozogamicin (product name Mylotarg) targeting CD33, and so forth have been developed. Further, for epithelial solid cancer such as breast cancer, trastuzumab (product name Herceptin) targeting Her2/neu, bevacizumab (product name Avastin) targeting VEGF, and so forth have been developed. Besides, for target diseases other than cancers, such as Rheumatoid arthritis and Castleman's disease, tocilizumab (product name Actemura) which is a human IL-6 receptor antibody, and so forth, have been developed.
However, the number of antibody drugs approved by 2008 is approximately 20 in the United States and approximately 10 in Japan. Particularly, against solid cancers, only few antibody drugs are effective. Hence, further development of effective antibody drugs is desired.
Meanwhile, “Homo sapiens podocalyxin-like (PODXL), transcript variant 2 (NM—005397.3)” (hereinafter, referred to as “PODXL2”) is known as a type I transmembrane glycoprotein which exists in a cell membrane and which has a highly glycosylated extracellular region. The human-derived PODXL2 molecule is identified as a glycoprotein homologous molecule of a rabbit podocalyxin molecule glycosylated with a foot process of a glomerular epithelial cell (podocyte), at human glomerular foot process and endothelial cell surface (Non Patent Literatures 1, 2).
Since having an N-terminal extracellular region subjected to characteristic glycosylation, PODXL2 is classified into sialomucin family. To the family, those expressed in hematopoietic cells or hematopoietic microenvironments (vascular endothelial cell and the like), such as CD34, CD164, CD162, CD43, and Endoglycan, belong. Homologous molecules of PODXL2 have been found so far in rat, rabbit, mouse, and human. The presence of a PODXL2-like molecule is expected in other vertebrates, also. Since having a similar tissue localization, these molecules are expected to be molecules having a similar function. Nevertheless, it is known that the N-terminal amino acid sequence considered as an extracellular region is less conserved among species.
Meanwhile, Miyajima et al. have revealed the presence of a hemangioblast that is a common precursor of a blood cell and a vascular endothelial cell in an AGM region (Aorta-Gonad-Mesonephros) where adult hematopoiesis is to occur. Further, a method of isolating and culturing a hemangioblast is established, and a mouse PODXL homologous molecule (PCLP1) is identified by expression cloning using a monoclonal antibody against a surface antigen on a mouse AGM-derived cell line. When fractioned and cultured in vitro, PCLP1 positive/CD45 negative cells are differentiated into endothelial-like cells, angioblast-like cells, and hematopoietic cells. Moreover, when PCLP1 positive/CD45 negative cells are transferred into a mouse defective in a hematopoietic function, a hematopoietic system is reconstructed over a long period of time. These facts indicate that the PCLP1 positive/CD45 negative cells contain mammalian hemangioblasts capable of expressing the activity of long-term repopulating hematopoietic stem cells (LTR-HSC). It is revealed that PCLP1 functions as a marker of a hemangioblast that is a common precursor to a blood cell and a vascular endothelial cell (Patent Literatures 1, 2 and Non Patent Literature 3). In addition, by microarray analysis and the like, PCLP1 has been found as one of genes having differences in an expression before and after differentiation of a stem cell, or in foamy cell differentiation, angiogenesis, and the like (Patent Literatures 3 to 6).
As to an antibody against PODXL2, utilization thereof in separation and amplification of a hematopoietic stem cell and the like has been disclosed (Patent Literature 7). In addition, measurement using an antibody against PODXL2 as a diagnosis marker for a kidney disorder has been disclosed (Patent Literature 8). Moreover, since PODXL molecules have various splicing forms in cancer cell systems, utilization in treatment and diagnosis with antibodies corresponding to these forms has been suggested (Patent Literature 9).
However, any of these literatures do not disclose an example regarding an antibody which demonstrates a therapeutic effect on a specific disease by targeting PODXL2. It has not been revealed whether or not an antibody against PODXL2 has an anti-cancer activity.